A wide variety of turbine devices have been developed in order to remove energy from a flowing stream of fluid. Ancient watermills and windmills attest to man's age-old quest to ease the burdens of manual labor by wresting power from moving fluids. Man's attempt to obtain useful energy from wind and water has covered a wide spectrum of methods and applications. Historically, and by way of example only and not limitation, much of the progress has been made as a result of man's experience with sailing vessels. Early attempts to capture the wind's energy on land utilized sails made from fabric and stretched over some wooden framework to present a larger and lighter surface to react with moving air. Two basic wind turbine categories have evolved which classify all efforts to date for the recovery of power from moving fluids such as air.
The first, and older, category is one that features devices that simply occupy space in the wind stream and obtain energy by the impact of the air molecules on their surface. These are referred to as “drag” type devices. Drag is a force that results from the turbine blade's action to slow the wind by obstruction. Some of the kinetic energy that air molecules possess by virtue of having both a mass and a velocity is transferred to the wind turbine blade by means of a collision in which the air molecule is slowed and the turbine blade is accelerated.
Historically, drag type wind turbines have utilized some fixed configuration of turbine blade that presented two differing aspects to the wind stream depending on which orientation was presented to the wind. It is the differential value of the drag forces operating on the two differing configurations that is responsible for the torque moment or turning force of the turbine. In prior art drag type turbines, the drag force differential was small because the cross-sectional area presented to the wind was the same in both directions and only the configuration (concave or convex) varied much. Another typical characteristic of most drag type prior art devices is a shortened moment arm for each turbine blade. Rate of rotation has always been a prized value and extending the moment arm reduces this value as it increases torque.
One example of a common prior art drag type device is the anemometer used to measure wind velocity. In most anemometers, hollow hemispheres are mounted on spars that connect to a shaft which turns as the wind stream reacts with the hemispheres on each side of the axis of rotation. Due to their opposite orientation with respect to the wind stream, there is a differential between the drag force on one side and on the other, with respect to the shaft about which they are free to rotate. This drag differential results in a torque about the shaft and the cups rotate about the shaft due to this torque. Almost all drag type devices utilize a set configuration that seeks to optimize this drag differential by utilizing shapes which move freely through the wind in one direction, but which catch the wind when rotated in the air stream.
The second, newer, category of turbine devices includes those devices that rely on a “lift” force that is obtained by the wind's interaction with a particular form or shape inherent in the geometry of the sail or turbine blade. Lift is obtained when an airfoil, preferably a clean, i.e. structurally uninterrupted, airfoil, separates the wind stream into two portions which are forced to travel at differing velocities due to the shape of the foil. In the portion of the wind stream that is a accelerated relative to the portion that is slowed, a lower air pressure is induced. This lowered pressure on one side of the airfoil relative to the other results in a force normal (perpendicular) to the wind stream against the high-pressure side of the airfoil.
Since lift type turbine devices have the potential to extract a greater portion of the wind stream's energy by virtue of the fact that they don't require a collision of the air molecules with the surface of the sail or turbine blade, most recent attempts to design energy producing turbines have featured this principle. Due to the geometry of the manner in which lift force is induced in a lifting airfoil, current wind turbines typically rotate in a circular plane that is normal to the wind stream and rotate about an axis that is parallel to the wind stream. Because most airflow near the earth's surface is horizontal, this means that the plane of the wind turbine's rotation must be oriented in a vertical position and that the derived energy is produced at the end of a horizontal axis originating at the center of the wind turbine. Since the direction of the wind stream's flow is variable, the plane of this type of wind turbine's operation must also be variable to enable it to continually face into the wind.
Further, because the wind turbine's plane of rotation is vertical, it must be supported above the earth's surface by some sort of tower whose height is at least greater than the radius of the wind turbine's circular plane of rotation. Furthermore, this tower is constrained to be of a structural, vertical cantilevered design, since guy wires would interfere with the rotation of the wind turbine blades. Still further, since the wind turbine's circular plane of rotation is vertical and so is the tower that supports it, each must be offset from the other to prevent collision of the two. These turbines also create an eccentric load on the tower adding further complication to their design. In order to balance the eccentric load and to make efficient use of the energy available at the end of the horizontal shaft located at the top of the support tower, most present-day/prior art designs call for a power transmission and electric generator to be mounted at the top of the tower and at the opposite end of the horizontal drive shaft from the wind turbine. These designs result in significant weight which must be supported by the tower, kept in balance, and allowed to turn as the wind changes direction. Further, the tower must also be designed to resist the total overturning moment caused by the wind resistance of the wind turbine, the hub assembly and the tower itself. Not only does the tower have to resist these loads, but the tower foundation must eventually resolve such loads by transference into the surrounding ground. These requirements severely limit the altitude above the earth's surface that such wind turbines can be operated.
Another major limitation of present-day turbine technology is the required configuration of the individual turbine blades. Such blades are airfoils that obtain lift by virtue of their shape as the wind passes around them. The optimum shape requires a long blade length, but a short blade cross-section. This high L/D ratio in conjunction with a requirement to maintain low mass (weight) needed for maximum acceleration sets conflicting limits on the design of the wind turbine itself. Current optimizations of these conflicting variables result in blade configurations that are at or near critical values in each category of variable and severely limit the range of operating environment that current turbines may safely experience. That is to say, modern wind turbine systems are rigged to monitor for environmental variables such as gusting, wind direction, wind velocity and wind shear (among others) and are set to feather or stop operation altogether should any of these variables exceed the design range of operation.
The prior art is replete with references to patents for both drag and lift type devices. Three such patents are representative. U.S. Pat. No. 4,264,279 describes a lift type turbine. Although this is a lift type design, it utilizes airfoils mounted horizontally on a vertical axis. Apparently, it operates as does an autogyro since it cites a self starting feature. U.S. Pat. No. 4,377,372 is illustrative of the drag type patents of the prior art. This device uses flat plates that are hinged in the middle to alter profiles presented to the wind. The hinged plates open by gravity and are closed by the force of wind alone. U.S. Pat. No. 5,823,749 is also for a drag type device. This device utilizes fabric vanes because of weight considerations, thereby making it inappropriate for high wind velocity environments. Nonetheless, the invention shows an improvement whereby opposing vanes are linked by cords. Thus, when one vane is opened by gravity, the attached cord pulls the opposite vane closed.
In summary, drawbacks to the turbines known in the art, and in particular to wind turbines known in the art, include the necessity for lightweight, and therefor fragile, construction and the resultant inability to take advantage of the vastly more productive high wind velocity environments. Further, except for rudimentary string/cord devices, no coordination between wind vanes exists so as to enable controlled opening and closing of vanes in all wind conditions and no coordination of the multiple wind vanes is provided at all. Still further, prior art devices must be stopped when winds exceed design limits or when gusty wind conditions exist.
Thus, there is a need in the art for providing a turbine capable of use in extreme conditions, ruggedly constructed, efficient and inexpensive in design, and wherein the individual turbine blades are connected to other turbine blades and their movements are coordinated. It, therefore, is an object of this invention to provide an improved turbine system for capturing energy from a fluid stream. In particular, it is an object of this invention to provide an improved wind turbine apparatus and method for operation in high air and gusty wind conditions.